docs: def Prandtl(Cp=None, k=None, mu=None, nu=None, rho=None, alpha=None):
      r'''Calculates Prandtl number or `Pr` for a fluid with the given
      parameters.
  
      .. math::
          Pr = \frac{C_p \mu}{k} = \frac{\nu}{\alpha} = \frac{C_p \rho \nu}{k}
  
      Inputs can be any of the following sets:
  
      * Heat capacity, dynamic viscosity, and thermal conductivity
      * Thermal diffusivity and kinematic viscosity
      * Heat capacity, kinematic viscosity, thermal conductivity, and density
  
      Parameters
      ----------
      Cp : float
          Heat capacity, [J/kg/K]
      k : float
          Thermal conductivity, [W/m/K]
      mu : float, optional
          Dynamic viscosity, [Pa*s]
      nu : float, optional
          Kinematic viscosity, [m^2/s]
      rho : float
          Density, [kg/m^3]
      alpha : float
          Thermal diffusivity, [m^2/s]
  
      Returns
      -------
      Pr : float
          Prandtl number []
  
      Notes
      -----
      .. math::
          Pr=\frac{\text{kinematic viscosity}}{\text{thermal diffusivity}} = \frac{\text{momentum diffusivity}}{\text{thermal diffusivity}}
  
      An error is raised if none of the required input sets are provided.
  
      Examples
      --------
      >>> Prandtl(Cp=1637., k=0.010, mu=4.61E-6)
      0.754657
      >>> Prandtl(Cp=1637., k=0.010, nu=6.4E-7, rho=7.1)
      0.7438528
      >>> Prandtl(nu=6.3E-7, alpha=9E-7)
      0.7000000000000001
  
      References
      ----------
      .. [1] Green, Don, and Robert Perry. Perry's Chemical Engineers' Handbook,
         Eighth Edition. McGraw-Hill Professional, 2007.
      .. [2] Cengel, Yunus, and John Cimbala. Fluid Mechanics: Fundamentals and
         Applications. Boston: McGraw Hill Higher Education, 2006.
      .. [3] Gesellschaft, V. D. I., ed. VDI Heat Atlas. 2nd edition.
         Berlin; New York:: Springer, 2010.
      '''
      if k and Cp and mu:
          return Cp*mu/k
      elif nu and rho and Cp and k:
          return nu*rho*Cp/k
      elif nu and alpha:
          return nu/alpha
      else:
          raise Exception('Insufficient information provided for Pr calculation')